Semimembranosus action includes which of the following?

• A. Flex the knee, medially rotate the flexed knee, extend the hip, medially rotate the hip, tilt pelvis posteriorly
• B. Flex the knee, laterally rotate the knee
• C. Extend the knee, medially rotate the hip
• D. Flex the hip, abduct the thigh

Answer: (A)

Semimembranosus is a two-joint muscle crossing both the hip and knee, so its actions include both extending the hip and flexing the knee. When the knee is flexed, it medially rotates the tibia, and it also medially rotates the thigh at the hip. Bilateral contraction can tilt the pelvis posteriorly.

This option matches those actions: knee flexion, medial rotation of the flexed knee, hip extension, medial rotation of the hip, and posterior pelvic tilt.

It doesn’t fit other ways because semimembranosus isn’t a knee extensor, so knee extension isn’t correct, and it doesn’t laterally rotate the knee or abduct the thigh; those actions are not characteristic of this muscle.